1. Technical Field
This invention applies to turbine engine rotor assemblies in general, and to apparatus for damping vibration within turbine engine rotor assemblies in particular.
2. Background Information
Turbine and compressor sections within an axial flow turbine engine generally include a rotor assembly comprising a rotating disk and a plurality of rotor blades circumferentially disposed around the disk. Each rotor blade includes a root, an airfoil, and a platform positioned in the transition area between the root and the airfoil. The roots of the blades are received in complementary shaped recesses within the disk. The platforms of the blades extend laterally outward and collectively form a flow path for fluid passing through the rotor stage.
During operation, turbine engine rotor assemblies rotate at a variety of speeds through fluid that varies in temperature, pressure, and density. As a result, the blades may be excited in a number of different modes of vibration. Lower order modes, such as the first bending mode and first torsion mode, are generally predictable enough such that a single style damper may be implemented throughout the rotor assembly. For instance, a particular style damper may be implemented against the blade platforms of adjacent blades to damp lower order vibration.
Higher order modes of vibration, on the other hand, are more difficult to damp. Upstream airfoils within a multiple stage rotor assembly, for example, can create aerodynamic wakes that cause downstream airfoils to experience higher order modes of vibration such as plate deformation. Plate deformation, predominantly in the form of chordwise bending, often manifests in upper regions of the airfoil in a non-symmetrical pattern and is accordingly difficult to predict in terms of magnitude and position.
What is needed, therefore, is an apparatus and/or a method for damping higher order modes of vibration in a blade of a rotor assembly.